USB-C monitor not detected

@TimmyGilissen  if you're curious, I wrote an explainer post about the various differentiating capabilities of USB-C cables here.  But basically, the most capable USB-C cable you can get today (ignoring Thunderbolt 3 cables) is one that supports USB 3.1 Gen 2 (10 Gbps), DisplayPort Alt Mode, and USB Power Delivery up to 100W.  But those cables right now are only available in lengths up to 1m / 3.3 feet.  The next step down would be a cable that supports USB 3.1 Gen 1 (5 Gbps), DisplayPort Alt Mode, and USB Power Delivery up to either 60W or 100W.  Those are available in lengths up to 2m / 6.6 feet.  Note that I do NOT recommend getting a Thunderbolt 3 cable here, partly because they're more expensive and would serve no benefit for regular USB-C, and also because longer Thunderbolt 3 cables are more likely to be "active" cables that are actually WORSE for regular USB-C, as I explained in the thread I linked above.

@TimmyGilissen  are you using a USB-C cable that specifically supports DisplayPort Alt Mode to carry video?  Some USB-C cables can only be used for USB 2.0 and charging.

The solution that worked for me

Hi,

I hope this works for you, I had this issue yesterday with my Dell Precision 5540 and Dell U3219Q monitor after a power outage where the display was previously working via the USB-C suddenly stopped. I tried searching the net but didn't find a solution and opted to use the HDMI port which worked, I also tested the USBC with my iPad Pro which worked perfectly. Today while I got it to work though so I wanted to share my solution that I found by chance:

Connect another display OR two of the Monitor inputs eg, the USBC and the HDMI.

Right click on desktop and Open "Dell Display Manager" (install it if you don't already have it)

It will display the summarized version, At the bottom click on "Open Dell Display Manager"

On the Basic Tab, right at the bottom mine showed a tick box that said something like "Enable display matrix control"

NOTE: My USBC was connected as well as the HDMI on the laptop at the time. I've tested it and this option only appears on the "Basic" tab if "Dell Display Manager" thinks that there is more than one external monitor. I connected both display outputs on the laptop to the same monitor which fooled "Display Manager" into thinking I had 3 displays, the laptop display a USBC display and an HDMI display. Found this totally by chance because I had the HDMI connected for the display and I was still using the USBC from the monitor to my laptop because the keyboard is connected to the monitor and then via the USBC to the laptop because when it was working I just had a single USBC cable to connect to my laptop for both display and keyboard. Hope this helps someone. Hopefully Dell also sees this and figures out why or updates the app the show the "Enable display Matrix" always.

Dell P2419HC Dell Display Manager User’s Guide

Hey

I am currently experiencing the same problem. Did you end up finding an answer?

Thanks

Hello, we see you are looking for assistance. Click our DELL-Cares username, on the right click, "Send this user a private message". Provide to us the private Dell PC Service Tag.

I found that dell set the bios (F2 at startup) to thunderbolt disabled, with a 'dell dock override' setting enabled that ensures dell docks and monitors work - I needed to enable all the thunderbolt options - and make sure to disable the 'dell dock override' as this seems to cause issues as well.

The device or dongle isn't connected to the correct USB-C port on your PC (or phone). The device or dongle is connected to your PC (or phone) using an external hub or dock. There are too many other devices or dongles connected to your PC (or phone) that use a USB-C connection.

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